<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    .son {
      margin: 10px;
      width: 100px;
      height: 100px;
      background: paleturquoise;
    }

    .normal {
      margin: 10px 0;
    }

    .son2 {
      margin: 10px 0;
    }

    .BFC {
      overflow: hidden;
    }
  </style>
</head>
<body>
  <div class="normal">
    <div class="son"></div>
  </div>
  
  <div class="BFC">
    <div class="son2">
      <div class="son2">
        <div class="son"></div>
      </div>      
    </div>
  </div>

  <div class="normal">
    <div class="son"></div>
  </div>

  <div class="normal">
      <div class="son"></div>
    </div>
</body>
</html>